In this study, the stool from either patients with CRC or control patients was gavaged into mice twice a week for 5 weeks. One group of mice had received azoxymethane (AOM) which induces neoplasia and the other group were germ-free mice. Extensive studies involving immunohistochemistry, expresssion microarray, quantitative polymerase chain reaction, immunoblot, and flow cytometry.

Key findings:

Conventional, AOM-treated mice who received gavage from patients with CRC had significantly higher proportions of high-grade dysplasia (P<.05) and macroscopic polyps (P<.01)

Among the germ-free mice fed with stool from patients with CRC, there was a higher proportion of proliferating Ki-67-positve cells

These findings correlated with more dysbiosis in the mice who received stool from patients with CRC and with upregulation of genes involved in cell proliferation, stemness, apoptosis, angiogenesis, and invasiveness

“This study provides evidence that the fecal microbiota from patients with CRC can promote tumorigenesis in germ-free mice and mice given a carcinogen.”

My take: This study shows that microbiota clearly influence the risk of CRC. I infer from this study that this could explain the potential healthy roles of diets with more fruits and vegetables, that promote healthier microbiota as well as the potential detrimental role of diets with more processed meats.

In mice, studies have shown that low-dose penicillin in early life induces marked effects on body composition (eg. excessive weight gain) lasting into adulthood

Prenatally administered penicillin to the mother and high-fat diet also induced fat mass of male mice.

Gut microbiota transferred from penicillin-moderated flora mice (at 18 weeks) into the cecums of 3-week-old germ-free mice also resulted in excessive fat mass compared to controls who received gut microbiota transfer from control mice (who did not receive penicillin).

“These results suggest that immunologic and metabolic changes are not caused by direct effects of antibiotics but rather by derived changes in the gut microbiota.”

“It may even be speculated that in families in which obesity is a problem, specific antibiotic treatment at birth could reverse the adverse effect of obesogenic microbiota transferred from mother to infant during delivery.”

Take-home message: Understanding the microbes in our bodies may lead to much more than curing intestinal infections and intestinal maladies.

A recent study (J Pediatr 2014; 165: 23-9) confirmed the obvious: “early empiric antibiotic use in preterm infants is associated with lower bacterial diversity.” That being said, you still need the data and the specific changes are of importance.

This study examined the stools from 74 preterm infants (≤32 weeks gestational age) and determined how the microbiota changed in relation to no antibiotics (18% of cohort), brief antibiotics (1-4 days) (64% of cohort), or ‘intensive’ antibiotics (5-7 days) (18% of cohort). Empiric antibiotics consisted of ampicillin and gentamicin. Stools were analyzed with the 16s ribosomal DNA community profiling.

The key findings are graphically shown in Figure 1 with pie charts showing the relative abundance of 10 bacterial genera at week 1, week 2, and week 3 in each of the three groups.

Those who received 5-7 days of antibiotics had the most changes in their microbiota with increased Enterobacter and lower bacterial diversity in the second and third weeks of life.

In those who received no empiric antibiotics there was increasing bacterial diversity noted sequentially. These changes were not seen in either of the antibiotic groups. However, the group with brief antibiotic exposure returned to their baseline diversity by week 3.

Infants receiving early antibiotics experienced more cases of necrotizing enterocolitis, sepsis and death than those who were not exposed to antibiotics (this was not proven to be casually-related).

Take-home message: This study proves that antibiotics change the microbiome in neonates and that neonates exposed to antibiotics may have complications as a result. Better biomarkers (with rapid turn around time) would allow more careful selection of which neonates need empiric antibiotics.

PMN CD64 was significantly elevated in CD compared with non-IBD controls and correlated with mucosal injury as measured by the simple endoscopic score for CD.

Patients in clinical remission with a PMN CD64 <1 had a high rate of sustained remission (95%) whereas only 56% had sustained remission if PMN CD64 was >1.

Take-home point: This study shows in pediatrics, as in adults IBD patients, that PMN CD64 index is associated with mucosal inflammation; high levels are associated with clinical relapse. Serum biomarkers are likely to complement stool biomarkers like fecal calprotectin.

One other point the authors make: “studies have found that 57% to 59% of CD have concurrent IBS.” Thus, there is a need for biomarkers to distinguish whether patients with clinical symptoms are experiencing an inflammatory relapse.

“Alterations in the Intestinal Microbiome (Dysbiosis) as a Predictor of Relapse After Infliximab Withdrawal in Crohn’s disease” pages 978-86. N=33 CD patients. Key finding: “CD-associated dysbiosis, characterized by a decrease in Firmicutes, correlates with the time-to-relapse after infliximab withdrawal.”

A recent editorial (NEJM 2013; 368: 1647-49) helps explain the link between diet, genes, and gut microbes. This editorial places in context a study, NEJM 2013; 368: 1575-84). “The investigators found than dietary choline is metabolized by gut microbes to trimethylamine (TMA), which in turn is absorbed into the host bloodstream and metabolized in the liver to trimethylamine-N-oxide (TMAO).” TMAO is thought to promote atherogenesis.

The study involved two phases. In the first, using mass spectrometry, before and after suppression of gut microbes with antibiotics, they showed that a phosphatidylcholine challenge increased all choline metabolites; however, antibiotic use suppressed the formation of TMAO.

In the second phase, they looked at fasting plasma TMAO in relation to cardiovascular events in more than 4000 participants who underwent elective coronary angiography. They identified an “independent, dose-dependent relationship between TMAO and the risk of a cardiovascular event.”

TMAO levels depend on the interaction between gut microbial production of TMAO which is affected by diet and by host genetic factors. The genetic factors are related to flavin-containing monooxygenases (FMO1 and FMO3); these enzymes oxidize TMA to TMAO are vary significantly in mice (and probably humans). With regard to diet, by limiting choline-rich foods (see links below regarding choline-rich foods) or by using probiotics, this may limit TMAO production and lower the risk of heart disease.

While these observations are intriguing, the mechanisms of TMAO in causing atherosclerosis and its primary function are unknown and much more information is needed to truly make these findings useful. It is possible that TMAO is simply a biomarker of other factors.

One aside, the editorial states that our gut microbes contain “at least 100 times as many genes as our own genome.”

Take-home message: TMAO is a new potentially modifiable risk factor for atherosclerotic disease.

Maybe your mother was right –you should eat your vegetables! For a long time, it has been known that dietary changes can be used to treat Crohn’s disease. The specifics about what type of diet and the reasons for how diet promotes a healthy gastrointestinal tract are being unraveled. A person’s diet affects their microbiome; and, a number of recent articles have highlighted the microbiome in both functional and nonfunctional disorders (see below).

An even more fascinating article is in last week’s New England Journal of Medicine (NEJM 2012; 366: 181). This article discusses two publications which show how certain dietary components interact with intestinal immune receptors.

Kiss EA et al. Science 2011 October 27 (Epub ahead of print).

Li Y et al. Cell 2011; 147: 629-40.

This NEJM article implicates a typical ‘Western’ diet as a contributor to inflammatory bowel disease (IBD). However, a diet high in vegetables may prevent or reduce inflammation. One mechanism whereby vegetables affect the GI tract is through the AhR (aryl hydrocarbon) receptor. Some vegetables, like broccoli, cabbage, and brussel sprouts, are natural ligands for this receptor. A mouse model has shown that AhR deficiency “results in increased epithelial vulnerability, immune activation, and altered composition of the microbiota.” In addition, AhR is down-regulated in the intestinal tissue of persons with IBD. AhR ligands are associated with increased interleukin-22 which promotes intestinal integrity.

Additional work regarding the optimal diet are ongoing. There has been an interest in a ‘carbohydrate specific diet.’ This year’s NASPGHAN meeting (abstract #48) presented data on this diet from a retrospective study. This poster described five patients on monotherapy (diet alone) and at 6 months –good results in four patients (80%). A few prospective studies are underway; in fact, a prospective study with patients from our office will be presented at this year’s DDW. Initial results look promising (personal communication from lead investigator, Stan Cohen).

In this month’s Gastroenterology, two articles offer some insight into this question for two separate problems.

With regard to inflammatory bowel disease, (IBD) –both Crohn’s disease and UC –there is an increasing prevalence and incidence worldwide (Gastroenterology 2012; 142: 46-54). This article identified 8444 previous citations and then identified 262 studies with relevant data. Overall, the highest incidence and prevalence of these disorders occurs in Europe and North America. In North America, Canada has the highest prevalence with 0.6% of the population having IBD.

After going through the statistics, the authors offer some discussion on why IBD is increasing. In the developing parts of the world, some of the increase is due to the ability to detect and differentiate these disorders due to improving access to medical care/colonoscopy. In the areas of the world with the highest incidence/prevalence, environmental risk factors are playing an important role. Potential factors include microbial exposures, sanitation, lifestyle behaviors, medications, and pollution. These factors are supported by other epidemiological studies which show that individuals who move from low prevalence areas to higher ones are at increased risk for IBD, especially among first generation children (Gut 2008; 57: 1185-91). Furthermore, in low prevalence regions, IBD is increasing with more industrialization (Chin J Dig Dis 2005; 6: 175-81, Indian J Gastroenterol 2005; 24: 23-24.) Exact mechanisms are poorly understood; however, even in the U.S. it is recognized that rural/farm exposure at a young age reduces the likelihood of developing IBD at a later age (Pediatrics 2007; 120: 354).

Celiac disease, likewise, has seen an increase in prevalence. With celiac disease, the proliferation of widely available and more accurate serology has been crucial in the identification of more patients. However, like IBD, there is likely a role for changing microbial environment contributing to an increasing case burden. Recently, reports have shown that the risk of celiac disease can be influenced at birth (Gastroenterology 2012; 142: 39-45). Although the absolute risk was modest, there was an increased risk demonstrated with elective but not emergent cesarean delivery among a large nationwide case-control study from Sweden. Among the cohort of 11,749 offspring with biopsy-proven celiac (with matched control group of 53,887), elective cesarean delivery resulted in an odds ratio of 1.15 (confidence intervals 1.04-1.26). This study confirmed other studies which have shown an increased risk with cesarean delivery (Pediatrics 2010; 125: e1433-e1440). Some of the strengths of this Swedish study, included the fact that the deliveries were separated based on elective or emergency cesarean delivery and were controlled for whether the mother had celiac disease. (Pregnant women with celiac disease have an increased risk of cesarean delivery.) The authors speculate that the reason why elective cesarean deliveries increase the risk of celiac disease is that microbial exposures at birth likely influences perinatal colonization –>affects intestinal immune response and mucosal barrier function. Offspring of women with emergency cesarean delivery would be more likely to be exposed to bacteria from the birth canal and no significant increase risk of celiac disease could be identified in this group.

Thus how we are born and where we live make a big impact on the likelihood of developing these GI disorders.